Yamaha VK540EF, Service Manual, Page: 110 / 439

2-35
CARBURETOR TUNING
INSP
ADJ
ESS00090
Main jet selection chart
Main jet selection chart
Spark plug color Diagnosis Remedy
Light tan or gray Carburetors are
tuned properly.
Dry black or fluffy
deposits Mixture is too rich. Replace the main jet with the next smaller
size.
White or light gray Mixture is too lean. Replace the main jet with the next larger
size.
White or gray
insulator with small
black or grayish
brown spots and
electrodes having
a bluish-burnt
appearance Mixture is too lean.
The piston is
damaged or seized. Replace the piston and spark plug.
Tune the carburetors again. Begin with
low-speed tuning.
Melted electrodes
and possible a
blistered insulator
Metallic deposits on
insulator Mixture is too lean.
The spark plug
melted. Check the piston for holes or seizure.
Check the cooling system, gasoline octane
rating and ignition timing. After replacing
the spark plug with a colder type, tune the
carburetors again. Begin with low-speed
tuning.